1. Field of the Invention
The present invention relates to antistatic electronic packaging articles, such as integrated circuit trays, packaging, and the like, specifically to an electronic packaging article having antistatic and protective coating(s) comprising a vanadium pentoxide, a polymer latex having a hydrophilic functionality, and a nonsulfonated protective topical binder.
2. Description of the Art
The traditional means of protecting sensitive electronic components from electrostatic energy has been the use of either ionically conductive coatings, i.e., surfactants, or conductive particulate filled plastics. Electrically active plastic composites use highly conductive fillers, such as particles, fibers or flakes in an insulative polymeric base resin. Commonly employed electrically active fillers include carbon powder, carbon fiber, metal powders, fibers and flakes, and metallized particles, fibers and flakes. These are disclosed in multiple patents, e.g., U.S. Pat. Nos. 4,634,865, and 4,288,352.
However, while useful, conductive particles suffer from some drawbacks. They are very expensive to make and use, and the expense is heightened due to the fact that such particulates are present throughout the volume and not just on the surface where the electrostatic dissipation (ESD) is required. It can also be difficult to control the conductivity due to the percolation phenomenon of the conductive media in the insulative matrices. The sensitive balance between the conductive filler and the insulative resin is further complicated by injection molding processes which cause variations in polymer/fiber orientation, density, shear and cooling rates.
A cheaper traditional technique of providing antistatic protection for electronic components has been the use of ionically conductive antistatic coatings thereon. These coatings provide a thin electrolytic film on the articles' surface by drawing moisture from the air. Mobility of ions in the film conducts electricity. However, these coatings have the disadvantage of lack of permanency; i.e., they may wash off or wear off, and their ESD protective properties are highly humidity dependent. Further, such coatings can be a contamination problem for electronic components.
More recently, the use of colloidal vanadium oxide colloids as antistatic coatings has been disclosed for a variety of uses has been disclosed. U.S. Pat. No. 4,203,769, discloses preparation of an antistatic layer from an aqueous composition comprising vanadium oxide. The composition may also contain a binder to improve the mechanical properties of an antistatic layer, such as cellulose derivatives, polyvinyl alcohols, polyamides, styrene copolymers, maleic anhydride copolymers, copolymer latexes of alkylacrylate, vinylidene chloride and itaconic acid, for photographic film or paper. The layer comprises at least 80%, preferably 100% vanadium pentoxide, which is prepared and recovered as an aqueous solution. The antistatic layer preferably is overcoated with a protective layer containing a cellulose compound.
U.S. Pat. No. 5,221,598 discloses a base for a photographic element which comprises a support, a vanadium pentoxide antistatic layer and an overlying barrier layer of a heat-thickening polyacrylamide polymer having hydrophilic functionality, and the photographic element, along with optional adjuvants such as gelatin, hardening agents, wetting agents, matte particles and the like. The protective layer prevents the diffusion of vanadium pentoxide out of the antistatic layer. The Examples reveal that the samples had excellent antistatic properties, and adhesion to the gelatin layer after 30 seconds and 60 seconds in developing and fixing solutions.
U.S. Pat. Nos. 5,356,468, 5,006,451, and 5,366,544 disclose a photographic element containing a vanadium pentoxide antistatic layer, and various binders; e.g., a cellulose acetate binder, a cellulose nitrate designed to prevent precipitation of the vanadium pentoxide out of the film base during precipitation and fixing.
The above photographic coatings need not have low surface resistivity, a critical issue in integrated circuit IC) handling, but need only have low internal resistivity.
Low-melting water-dispersible sulfopolyesters are disclosed for use in coatings, useful for stain release, photographic sublayers, adhesives, and the like in U.S. Pat. Nos. 3,734,874, 3,779,993, 4,052,368, 4,304,901 and 4,330,588.
U.S. Pat. No. 4,203,769 discloses an vanadium pentoxide colloid coating useful in photographic sublayers, magnetic recording films, and a wrapping for radiographic materials where the vanadium pentoxide colloid is coated onto lead coated paper, followed by a coating of cellulose acetate.
WO 93/24322 discloses the use of a vanadium oxide coating in packaging materials.
U.S. Pat. No. 5,407,603 discloses a process for the preparation of vanadium pentoxide colloidal dispersions which contain high aspect ratio particles, and are aged after formation of the dispersion for up to 8 days. The dispersions are disclosed to yield coatings having more effective antistatic decay properties while using lesser concentrations of vanadium oxide, antistatic coatings are disclosed.
Two embodiments have now been discovered that provide both an antistatic coating and a protective coating which insures longevity of the antistatic properties. Both embodiments provide a long lasting static dissipative electronic packaging article inexpensively, in contrast to conventional coated articles which suffer from the need to renew the antistatic coatings. Both embodiments provide noncontaminating, electrically conductive environmentally independent permanent antistatic coatings.
In one embodiment, a two layer coating is provided; the first layer being an V.sub.2 O.sub.5 antistatic coating comprising the vanadium pentoxide and a minor amount of a polymer latex having a hydrophilic functionality; the second layer being a nonsulfonated protective topical binder.
In the second embodiment, it has been discovered that the nonsulfonated protective topical binder may be added directly into a V.sub.2 O.sub.5 antistatic coating which also comprises a polymer latex having a hydrophilic functionality. The inclusion of the nonsulfonated protective topical binder provides a single layer antistatic/protective coating which exhibits improved permanence and humidity independence over the use of a single vanadium pentoxide-containing antistatic layer not containing such a topical binder.